Q: I made a couple of small cabinets from red oak lumber that I inlaid with cocobolo strips. I decided to use polyurethane to finish the project because I desired its durability. Curiously, the polyurethane cured fine where it was applied to the the oak but remained sticky and never seemed to dry over the cocobolo strips. What kind of finish can I use that will work well for both woods, while also maintaining a protective finish?
You have several options but let’s start by explaining why the one you used failed. Cocobolo is a dalbergia, a member of the rosewood family. Those woods contain an antioxidant that prevents the cure of finishes that depend on oxidation to cure. That includes everything from pure linseed oil through Danish oil and on up to oilbased polyurethane.
What you can use is any finish that cures by solvent evaporation, including shellac, lacquer and most waterbased coatings. Those will all cure quite nicely on both the oak and cocobolo. Another interesting option is to prime the wood with one coat of clear primer. I’d suggest Zinsser SealCoat™, which is made of dewaxed shellac. Once that coat dries, and it will, even on cocobolo, you can go over it with whatever finish you choose, including the oil-based polyurethane that did not dry when applied directly onto the cocobolo.